This circuit is for traditional old-style telephone lines found in an American 1980s documentation. Components are common and the optical coupler can be replaced with an equivalent.
This power supply may have 5, 6, 9 or 12 V outputs depending on the 78XX and 79XX series...
Other series amplifiers such as the MC3301, MC3401 and LM2900 can be used on this circuit. We...
This traditional doubler configuration with the 555 can be found in other articles on the author’s site....